This invention relates to printheads for ink jet printing apparatus, and more particularly to a printhead of this class having a plurality of jet orifices arranged in a matrix for discharging droplets of ink to print alphanumeric characters or other symbols on a surface moving past the printhead.
Reference may be made to U.S. Pat. Nos. 4,215,350, 4,378,564, 4,542,386, 4,450,375, 4,555,719 and 4,576,111 for their disclosures of printheads of this class.
Cross-reference may be made to the copending coassigned U.S. Pat. application Ser. No. 851,347 filed Apr. 14, 1986 for a disclosure of a printhead on which, in certain respects, the present invention is an improvement.
Among the several objects of the invention may be noted the provision of an improved printhead of the class described which has a relatively simple, compact, integrated ink jet orifice structure in which the ink jet orifices may be relatively closely spaced for printing relatively small characters; the provision of such a printhead which is reliable in operation and capable of ink jet printing with accurate, well-defined character formation; the provision of such a printhead which has relatively few moving parts, may be manufactured at relatively low cost, and which is easily dissassembled for cleaning, when necessary; and the provision of such a printhead which is capable of adjustment to compensate for tolerance variations, and for accurate control of the droplets.
The printhead of this invention thus comprises a body with a recess in its back face. A plurality of bosses extend back from the bottom of the recess with an orifice extending through each boss. A flexible membrane is mounted over the recess to form a chamber for ink supplied from a source under pressure. The membrane can engage the back ends of the bosses for closing the back ends of the orifices. The bosses and orifices are arranged in a close-spaced matrix.
Means is provided to hold the membrane against the back end of each boss and selectively release the membrane to allow it to flex away from the boss to deliver a drop of ink from the chamber to the orifice. This means comprises a slender, elongate member for each boss, the inner end of each elongate member being aligned with its respective boss and thus being arranged in a close array corresponding to the matrix. Means at the outer end of each elongate member, operating via the elongate member, releases the membrane. These release means are larger than the spacing of the bosses and cannot be aligned therewith, and therefore are arranged in a spread-out array with the elongate members extending from the closely spaced array at their inner ends to the release means in their spread-out array.
In a first embodiment, the elongate members are air tubes, and the release means are valves. Each valve is supplied with air under pressure. When the valve is not energized, the air is supplied to the tubes so the pressure holds the membrane against the respective bosses. When the valve is energized, the air supply to the tube is momentarily cut off, momentarily releasing the membrane and allowing a drop of ink to pass from the chamber to the orifice.
In a second embodiment, the elongate members are flexible wires having heads for pressing against the membrane and the release means are solenoids. The solenoids, when energized, momentarily pull the wire and the respective head away from the membrane, releasing the membrane and allowing a drop of ink to pass from the chamber to the orifice.
Other objects and features will be in part apparent and in part pointed out hereinafter.